Kemarin rencana ingin downgrade php5.3 ke php5.2,
OS yg digunakan pakai Debian6.0.1 dan menggunakan source.list milik ubuntu karmic,, hehe
Langsung saja penampakan errornya.
W: GPG error: ftp://ftp.itb.ac.id karmic Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: ftp://ftp.itb.ac.id karmic-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: ftp://ftp.itb.ac.id karmic-security Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: ftp://ftp.itb.ac.id karmic-backports Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: ftp://ftp.itb.ac.id karmic-proposed Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
Lansung saja.
Terlihat diatas error NO_PUBKEY 40976EAF437D05B5
Solusi,
#sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys key_yg_diminta
Contoh
#sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
# apt-get update
Done
Semoga bermanfaat :D .
Sumber
_http://juranktech.com/2011/03/05/fix-gpg-errors-saat-update-ubuntu/